Pulp bound compacted fuels

ABSTRACT

COMPACTED AND BOUND SOLID PARTICLES, FOR EXAMPLE FUELS SUCH AS BARBECUE BRIQUETTES AND FIREPLACE LOGS MADE FROM PARTICULATE COMBUSTIBLE MATERIALS SUCH AS SAWDUST, WOOD FLOUR, CHARCOAL, AND COKE IN WHICH THE BINDER FOR THE COMBUSTIBLE MATERIALS IS CELLULOSE FIBRES DERIVED FROM PAPER PULP.

Aug. 13, 1974 c. c. CRAWFORD PULP BOUND COIPACTED FUELS Original Filed larch 29, 1-967 wmEQ mcmmoxoua Eco wmSoE 25 Qwuwwu Em 50E INVENTOR. CHESTER c. CRAWFORD ATTORNEYS Emma 9525 5 2 m uoo United States Patent Ofiice 3,829,297 Patented Aug. 13, 1974 US. C]. 44-15 D 5 Claims ABSTRACT OF THE DISCLOSURE Compacted and bound solid particles, for example fuels such as barbecue briquettes and fireplace logs made from particulate combustible materials such as sawdust, wood flour, charcoal, and coke in which the binder for the combustible materials is cellulose fibers derived from paper pulp.

This is a continuation of patent application Ser. No. 870,313, filed Sept. 29, 1969, entitled Pulp Bound Compacted Fuels, which in turn is a continuation of patent application Ser. No. 626,739, filed Mar. 29, 1967, similarly entitled Pulp Bound Compacted Fuels, both now abandoned.

This invention relates to particulate solid materials bound by cellulose fibers derived from paper pulp.

In the preferred embodiment, the invention provides compacted combustible fuels such as briquettes for barbecuing, fireplace logs, fuels for space heaters, and the like. In the broadest aspects of the invention any type of particulate solid can be bound by the novel binder of the invention. For purposes of illustration, the preferred embodiment involving combustible fuels will be discussed initially.

The usual process for the manufacture of compacted fuels suitable for use in barbecue grills and braziers involves the blending together of finely ground charcoal, sawdust, wood chips, coke, or other combustible material in a thick slurry to which 4-15 of a cereal binder such as corn, tapioca, potato or other starch has been added. Under the mixing conditions employed, the cereal binder assumes a sticky gelatinous consistency which in subsequent operations such as briquetting, extrusion or other means for compressing the mass serves to cement or bind the various ingredients together. The products are ready for use following a drying step.

The present invention generally follows the existing art of compacted fuel manufacture while providing improvements in a number of aspects. The principal area of novelty lies in the use of a new binder system as a replacement for the usual cereal binders. In the broadest aspects of the preferred embodiment, the invention provides a compacted fuel containing a combustible material in divided form having a binder of pulp-derived cellulose fibers. For optimum results, the pulp is prepared from slick paper which is available in large quantities as waste mate rials in the form of book and magazine paper, for example.

In one aspect of the invention the pulp binder is used in combination with various blends of organic, combustible materials in a divided or ground form. One application involves a high proportion of coal or petroleum coke as the major non-binder combustible ingredient. Desired combustion rates are obtained by the inclusion of ignition accelerators, by the physical form of the coke, and byincluding a balancing proportion of high volatile combustible materials such as sawdust.

In another aspect, the invention provides a fast igniting, clean-to-handle fuel as distinguished from the difiiculty in lighting and dirtiness normally associated with wood charcoal compacted fuels. In this regard, a small proportion of the compacted fuel units is prepared with a relatively large percentage of high volatile combustible material. All of the compacted fuel units are coated with a suitable wax coating so that they can be readily handled without removing the dirt-causing ingredients from the surfaces. In use, rapid combustion is achieved by virtue ofthe compacted units formed from the high volatile materials.

The accompanying drawing contains a flow sheet describing one suitable method for preparing fuel units. Details of the invention will be described in connection with the flow sheet.

Suitable combustible materials in divided or ground form such as ground coke, wood flour, and ground charcoal are supplied and elevated for placement into bins. The material listed in the flow sheet are typical of the variety of combustible materials that can be used. A few other examples are sawdust, bagasse, rice hulls, wood chips, and wood shavings.

The combustible materials are metered through conventional feeding devices at a preselected rate to obtain the desired composition in the blender or pug mill. Selection of appropriate proportions will be discussed herein after.

Concurrently, another feed line to the pug mill is used for input of the binder which is prepared from a material suitable for pulping into separated cellulose fibers. Suitable materials for pulping include both soft and hard woods, rags, cotton linters, waste newsprint, waste rope, recovered corrugated sheets, book and magazine paper, and the like. Slick paper obtainable from such sources as book and magazine paper is a preferred raw material for pulping for the reasons to be discussed.

The waste paper is supplied to a hopper and fed to a pulper which may be of the blender type. A suitable amount of water is supplied to the pulper from a storage tank by a pump. The storage tank also receives residual water from the compacter. Pulped paper is fed from a pulp storage tank to the pug mill for blending with the previously discussed combustible materials. The blended mass is then compacted as in a briquette press, for exampie. The shaped and compacted unit is then dried, stored temporarily as required, optionally packaged for the type of consumer contemplated, and suitably stored until shipped or used.

The major novel element in the above scheme is the pulp-derived binder. It will necessarily be fed to the plug mill and compacted with the other ingredients in an amount sufiicient to cause retention of the compacted form of the fuel unit after discharge from the compactor to the drier. In general, he critical minimum amount of pulp fiber necessary for this job is about 5% by weight relative to the dried compacted unit. In general, there is no upper limit to the amount, even up to if desired. However, if the concentration of pulp is increased, the fuel tends to burn more quickly and does not liberate as much heat during the burning. In order to obtain more heat, components which will liberate more of the desired heat such as sawdust, charcoal, coal'or petroleum coke will generally be included. For instance, in making barbecue briquettes maximum heat and minimum flame is desired; it will prove advantageous to incorporate high percentages of the high heat content materials such as coke into the blend to constitute on the order of 65%, by weight or more with respect to the dried end product. For fireplace fuels, where more flame is usually desired, the concentration of high heat content material such as coke will normally be reduced to about 40-50% by weight of the dried unit and the concentration of higher volatile containing pulp and other combustibles will be proportion- Example 1.Preparation of Fireplace Logs 2.4 oz. of slick paper were pulped in 30 oz. hot water in a laboratory blender. (Slick paper is the type commonly found in magazines, and contains some added clay.) The resulting mass was transferred to a small laboratory mixer, and 4.8 oz. pine sawdust, finely ground, and 8.8 oz. of fluid petroleum coke added. These ingredients were then intimately mixed, and the procedure was re peated ten times to produce lb. of material (dry basis). The resultant product was charged to a pressure mold and compacted into the shape of an elongated cylinder, or logs, which on drying weighed about 1.25 lb. each. These logs had the composition: 1

Slic-k paper pulp percent by weight-.. Pine sawdust do 30 Petroleum coke do 55 Density of logs" 0.52

Bonding action of the pulp in the above-described logs was strong, and the finished product was virtually smudgeless. A stack of eight such logs, when burned in a fireplace, ignited readily and produced a cheery, blazing fire that lasted over two hours.

Example 2.Preparation of Barbecue Briquettes By the technique described in Example 1, barbecue briquettes having the following analysis were made up and tested: '5

Waste newsprint pulp percent 40.0 Petroleum coke, ground do 40.0 Wood charcoal ground do 20.0

Density 0.59

As in Example 1, bonding action was good."The briquetes were relatively smudge-free, and ignition was easy. A hot fire resulted.

Within the limits of the type of fuel being compacted in terms of heat liberation and flammability, the present invention provides the ability to utilize high proportions using in excess of 60% by weight of coke, whether of the petroleum or coal type, the present method contemplates finely grinding the coke prior to blending it with the other ingredients in the fuel. Optimum results are obtained 1 where the coke is ground so that at least about 75% of it will pass a 100 mesh screen. Where the coke content exceeds 60%, failure to observe this grinding limitation will result in a substantial portion of the coke not being burned. In general, the coke concentration should not exceed about 80% by weight of the fuel unit.

In addition to the preliminary grinding step of the coke, where the coke concentration is in the 60-80% range by weight of the fuel, an ignition accelerator will usually be required to accomplish a thorough burning of the fuel. The ignition accelerator is conveniently introduced illustrate through the water tank and dissolved therein for incorpo- Example 3.Preparation of Barbecue Briquettes 2.0 oz. of slick paper were pulped in 32 oz. of a 2.5% solution of sodium nitrate in water (hot). The resulting mass was transferred to a mixer where 2.4 oz. hardwood flour and 11.6 oz. finely ground petroleum coke through 200 mesh) was added. This procedure was repeated five times, and the total product combined. On pressing into briquettes and drying, the final product was found to be virtually smudge-free. It had the following analysis:

Slick paper pulp percent 12.5 Hardwood flour do 15.0 Petroleum coke do 70.0 Sodium nitrate do 2 5 Density 0.53

Three pounds of this product, when ignited in a barbecue grill, was ready for barbecuing in 20 minutes. The fire was hot and long-lasting.

This example was repeated by preparing the briquettes without grinding the coke to the extent indicated. In this case, the coke was ground so that 50% thereof was retained on a 100 mesh screen. When these briquettes were burned, a substantial portion of the coke was observed in an unburned condition at the end of the test.

Regardless of the composition and variety of the combustible components of the fuel unit, it is clear that a good bond between the combustible particles is important and is sought in all situations. As previously mentioned, an adequate bond is achieved by using sufficient pulp in the composition which in most cases will be in excess of 5% by weight of the dried unit and generally between 5 and 80% by weight. However, mere inclusion of the requisite amount of cellulose will not necessarily produce the type of product desired in terms of bonding strength. Analysis of the mechanism by which the cellulose pulp performs its role indicates that good bonding action occurs by virtue of an interlock between particles by individual cellulose fibers. The interlock is finalized during the compacting step. It further appears that the effectiveness of the interlock by the cellulose fiber is directly related to the length of the fiber as compared with the diameters of the particles of the combustible components. In the preferred em bodiment, this interlock is obtained if the average cellulose fiber length is at least as great as the average diameter of the particles to be bound. Preferably the cellulose fibers should be longer than the particle diameters. This size relationship is most conveniently accomplished by grinding of the fuel components other than the pulp to reduce the particle size to less than the cellulose fiber lengths. In this regard, better bonds will be achieved with finely divided particles such as wood flour, as compared with sawdust or planar shavings bound with the same cellulose fibers. Excellent results with respect to the bond can be achieved where all components in the mixture other than coke, if included, and the pulp are ground so that at least about 80% of the ground particles will pass a 20 mesh screen size.

Grinding of the combustible particles is only one way to achieve the noted size relationship between particles and cellulose fiber lengths. The other possibility is to select raw materials for pulping that will provide longer fibers. Slick paper is usually a relatively good grade of paper and contains cellulose fibers that are longer than, for example, those found in newsprint. Consequently, slick paper is a preferred type of raw material for pulping and use in the present invention. In addition to the longer fiber lengths, the slick paper provides an advantage by virtue of the normally occurring clay coating found on the paper which assists in the bonding action of the cellulose fibers. Other raw materials which provide longer fiber lengths such as rags would be a good choice for achieving a strong bond, but the availability and low cost of slick paper makes it a good choice balanced from all standpoints.

Another factor to be considered in achieving good bonding action is concerned with the amount of water utilized in preparing the cellulose pulp slurry. It is important that sufficient water be utilized in the pulping step to achieve a substantial separation of the pulp fibers. If there is an inadequate amount of water, the fibers are not completely separated and on compaction with the total formula results in an interlock between fibers instead of the interlock between fibers and particles. In general, the amount of water present during pulping should be suflicient to result in the presence of some free or separated water. The optimum situation is to have only a small or trace amount of free water so that the excess water need not be removed during subsequent drying. As long as there is some free water, the substantial separation of the fibers will be achieved. Experience has shown that a pulp slurry which includes about 3-8% cellulose content will provide the type of fiber separation which produces good bonds. In addition, where the water quantities are adjusted so that a water content of about 5075% by weight exists in the pug mill just before compaction, the separated condition of the fibers will be retained until compaction has been completed. Obviously, if in the initial pulping operation a good separation of the fibers is obtained, the separation can be lost if the water content is reduced so that the fibers recombine before use. The following example will illustrate the importance of maintaining at least about 50% water content at the blending stage in the-pug mill just prior to compaction.

Example 4.Preparation of Barbecue Briquettes Two batches of briquettes were prepared as described above, each having the following analysis (approx).

Percent Slick paper pulp 5.5 Pine sawdust 20.0 Ground petroleum coke 72.0 Sodium nitrate 2.5

Density 0.61

At the time of briquetting, one batch had only 45% water present. The bond of the resulting dried briquette was extremely weak. The briquette could be crumbled by hand and was unsatisfactory. The second batch (Density 0.70) at the point just prior to briquetting had 62% water, by weight. A little free water separated from the mixture prior to briquetting. The resulting dried briquette was strongly bound, could not be broken by hand, and was entirely acceptable.

The density of the finished dried compacted unit also has considerable effect on the strength of its bond and its ignition qualities. Where the density is too low, i.e., less than 0.50, for instance about 0.45, the fuel unit will exhibit some weakness of bond and will tend to crumble. Where the density is too high, i.e., above about 0.78, for example around .80-.83, the ignition properties are usually adversely affected and the product will tend to not burn easily or completely. Where the density of the end product is in the range of 0.50-0.78, optimum properties of bond strength and ignition are obtained for most types of fuels contemplated.

Adjustment of the density is achieved by proportioning the ingredients utilized. Density can be increased with more dense materials such as coke and decreased with less dense materials such as wood flour. By adjusting the amounts of these materials, the desired optimum densities can be obtained. In addition to adjusting the proportions of ingredients, the amount of pressure applied during the compaction step will affect the density and should be taken into consideration.

As noted above and illustrated in the flow sheet, following the compaction step, the materials are suitably dried to remove excess water. Any conventional type of drier can be used for this purpose. When drying the fuel units it is important to dry at temperatures not over about 375 P. so that the fuels are not subjected to combustion during the step. Drying should be continued for a time suflicient to reduce the water content of the fuel units to an lacceptable level on the order of about 5% by weight or ess.

In a preferred application of the invention, the dirtiness and tendency to smudge of most fuel units can be eliminated by applying a coating of a wax that will melt or burn at the temperature of a burning match, such as a paraflin wax, over the finished fuel units. For example, following drying of the fuel units they may be dipped in a bath containing liquified parafiin wax and then cooled to form a solid layer. While such a treatment by itself will completely remove all of the dirtiness associated with these types of compacted fuels, the difiiculty encountered is in achieving an easy ignition in burning of the fuels. To counteract the retarded combustion of the fuels two types of fuel units are mixed. The majority of the fuel units are made in accordance With the previous discussion in terms of the types of combustible materials and their amounts. A wax coating of not over 10% by weight and preferably not over about 56% by weight is applied to these units. In addition, a minor number of units, say on the order of 1 to about 6-10, of the normal units are prepared so that they are easily ignited and rapidly burned.

To this end, the ignition promoting units are prepared to contain only high volatile elements which are easy to ignite and thereafter burn rapidly. For example, such units can be prepared with a relatively high proportion of the high volatile pulp, together with some other high volatile such as sawdust. While a pulp unit would serve this purpose, for practical reasons a large proportion of some other materials such as sawdust will be used so as to minimize the amount of drying which will subsequently be required by the large water content of the pulp. A typical example of an ignition promoting fuel unit might contain about 25% by weight of pulp and about 75% of sawdust.

The ignition promoting fuel units are then given a relatively heavy wax coating of about 40-60% by weight of the finished fuel unit and perhaps as wide a range as 25-60% by weight. The user of a plurality of fuel units containing, say, one of the ignition promoting units for every six of the other type of units would be instructed to ignite the ignition promoting unit, which could be made identifiable by, for example, color. (It can be white while the other units are black.) The result would be that the user would sustain no discomfort from dirtiness and the like while handling the fuel units because of the wax coating. At the same time, lighting and burning of all of the fuel units would proceed readily and smoothly upon light ing with a match.

Consistent with the teachings in connection with the preparation of fuel units, the pulp binder can be used for binding or agglomerating any desired solid that is in a particulate form. As with the fuel unit, the desired results are obtained where the average size of the solid particle is no larger in diameter than the average length of the cellulose fibers. In general, the pulp binder will constitute a minor portion, i.e., less than about 50% by weight, of the end product and will be present in an amount to create the desired strength of both beyond compaction. As with the fuel units, the end product will generally require 7 at least about 5% by weight of cellulose fibers derived from paper pulp.

The solids to be bound can be either water soluble such as the orinary table salt and ammonium compounds illustrated in the following examples or water insoluble as the sand particles also illustrated in the following examples.

Example 5.-Salt Agglomeration Percent Cellulose pulp 63.4 Sodium chloride 36.6

Example 6.Sand Agglomeration 2.4 oz. of slick paper was pulped in water in a laboratory blender, as above. The resulting thick slurry was then transferred to a small mixer, and 13.6 oz. of common builders sand added. After mixing, the mixture was briquetted in a small laboratory press. After drying, a hard, strong white agglomerate resulted. They had the following analysis:

Percent Cellulose pulp 13.9 Common sand 86.1

Example 7.--Slow-Release Fertilizer 4.7 oz. of slick paper was pulped in 67 oz. water in a laboratory blender. The resulting thick slurry was transferred to a small mixer, to which was added the following chemicals:

Oz. Ammonium nitrate 20.0 Di-ammonium phosphate 20.0 Potassium chloride 20.0

After mixing, the mixture was briquetted into rectangular shapes, each /2 in diameter. After drying, these were cut into /2" squares, so that a /2" cube resulted. They were found to have the following analysis:

Percent Cellulose pulp 20.1 Ammonium nitrate 25.0 Di-ammonium phosphate 2.5.0 Potassium chloride 29.1

In terms of plant food content, the cubes contained 13.5% nitrogen, 13.2% P and 18.8% K 0.

To test the slow-release capabilities of the above-described cubes, about fifteen of them were buried in sawdust in a small wooden box without top or bottom, i.e., a frame, of dimensions 5.3 cm. wide and 27.0 cm. long. 24.5 oz. of water was then slowly poured over the sawdust, taking almost an hour for the action. It can be shown that this amount of water was equivalent to 2 inches of rainfall. After the rain, the cubes were recovered and dried. Their original weight was 2.8 02.; after the rain they weighed 1.6. oz. The resulting 1.2 oz. of weight loss amounted to 43% of the original weightf The additional portions of the fertilizer content can be leached out if the cubes are wetted one or more additional times in the same manner.

In Example 6, the sand agglomerate is generally useful in the construction industry as a building unit or in the preparation of various types of molds. Where water insolubility is desired, a small amount of a suitable waterproofing agent such as paraffin or oil should be added.

Examples 5, 6, and 7, are exemplary of the various types of solids that may be bound with paper, pulp fibers. A few additional examples include iron filings, broken glass and metal scrap.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is understood that certain changes and modifications may be practiced within the spirit of the invention as limited only by the scope of the appended claims.

What is claimed is:

1. A process for the manufacture of compacted fuel units from particulate solid material selected from the group consisting of coke, wood flour, charcoal, sawdust, bagasse, rice hulls, wood chips and wood shavings comprising the steps of: providing a material suitable for pulping into separated cellulose fibers; pulping said material into separated cellulose fibers with sufficient water to provide free separated water; blending said pulp with said particulate solid material in divided form where the average diameter of said material as divided is at most equal to the average length of said cellulose pulp fibers; compacting said pulp particulate solid material blend to form a unit of preselected shape; and drying said compacted unit, said pulp having a dry weight of at least 5% of the dry weight of all solid materials in said compacted unit, said particulate solid material having a dry weight of at least 60% of the dry weight of all solid materials in said compacted unit.

2. A process in accordance with claim 1 wherein said particulate solid comprises combustible material and said combustible material contains coke in the range of 60 to 80% dry weight and includes the step of grinding said coke so that at least about thereof passes a 100 mesh screen before blending with said cellulose pulp.

3. A process in accordance with claim 1 wherein said particulate solid comprises combustible material and said combustible material is selected from the group consisting of wood flour, charcoal, sawdust, bagasse, rice hulls, wood chips, and wood shavings, and said combustible is ground so that at least about thereof will pass a 20 mesh screen before blending with said cellulose pulp.

4. A process in accordance with claim 1 wherein said material suitable for pulping is pulped in an aqueous slurry in which the cellulose content is about 3 to 8% by weight.

5. A process in accordance with claim 1 wherein the water content of the blend of cellulose pulp and particulate solid material is about 50 to75% thereof.

References Cited UNITED STATES PATENTS 1,454,410 5/1923 Robinson 44-15 3,070,485 12/1962 Strickman 4413 X CARL F. DEES, Primary Examiner 

